Re: 1/6 or 1/8 wave

"khobar" <pnixon18@xxxxxxx> wrote in message
news:a6zph.60494$GH1.57236@xxxxxxxxxxxxxxx
I've seen a couple of Intes MK66's advertised - one 1/6 wave and the other
1/8. The 1/8th should be better, but could someone give me an idea of what
the visual difference between 1/6 and 1/8 might be? Is there an obvious
difference in image quality? And would either of these be all that
different
from, say, a Celestron or Meade 8" SCT or 7" MAK or even the Orion 150mm
MAK?

A true 1/6 wavefront PTV optic, if it is nice and smooth (perhaps 1/30
wavefront RMS) is a superb instrument. Yes, a 1/8 wavefront PTV that is
also nice and smooth (1/40 wavefront RMS), would do a bit better, but the
difference would not be huge, but might be apprecaited on those rare nights
when the skies are exceptionally steady.

Unfortunately, the PTV measurements do not tell the entire story, and the
makers often do not provide the RMS measurements.

The SCTs I've seen test results for have not been 1/6 wavefront PTV, but
generally in the 1/2 to 1/4 wave range. I haven't seen any interferometric
results from either of the Maks.

Clear skies, Alan

.